1. Field of the Invention
The present invention relates to a control unit having the function of suppressing knocking to occur in an internal combustion engine and, more specifically, to a control unit of an internal combustion engine achieving the precision improvement in knocking detection by removing a “noise to take place due to operation of an operating member such as fuel injection valve, intake valve or exhaust valve” that is superimposed on a “vibration waveform that is detected using a knocking sensor”.
2. Description of the Related Art
Conventionally, adopted is a control unit of an internal combustion engine having such a knocking suppression function as “to suppress the occurrence of knocking by detecting the vibration in a cylinder to take place due to abnormal combustion of an internal combustion engine using a knocking sensor to correct an ignition timing to the retard side, thereby suppressing the occurrence of knocking.”
In such a control unit of an internal combustion engine having such a knocking suppression function, first with respect to a vibration waveform of the internal combustion engine having been detected by a knocking sensor, an operation such as Discrete Fourier Transform (DFT: Discrete Fourier Transform) is performed to extract only the vibration component of a specified frequency.
This specified frequency is a frequency with which a vibration level due to occurrence of knocking can be detected with high sensitivity, and has preliminarily been selected.
Next, a peak value pkl in a predetermined crank angle range of the vibration component of the mentioned specified frequency is extracted.
Furthermore, a background level bgl corresponding to the average value of the peak value pkl is calculated by filtering the peak value pkl.
Incidentally, the mentioned predetermined crank angle range has preliminarily been set as the “range of a crank angle at which a vibration level due to occurrence of knocking can be detected with high sensitivity”, and is generally referred to as a knocking detection period.
Besides, a standard deviation sgm is calculated based on the peak value pkl and background level bgl, and a threshold thd for knocking determination is calculated based on the background bgl and standard deviation sgm by the equation of “thd=bgl+(K1×sgm)”.
Where, K1 is a predetermined coefficient for calculating a threshold thd for knocking determination.
When a threshold thd for knocking determination is calculated, subsequently, by the comparison between the peak value pkl and the threshold thd for knocking determination, the presence or absence of the occurrence of knocking is determined.
In the case of pkl≦thd, no occurrence of knocking is determined, and a knocking strength knk, being the magnitude of a vibration level due to occurrence of knocking is set to zero.
On the contrary, in the case of “pkl>thd”, an occurrence of knocking is determined, and a knocking strength knk is calculated by the equation of “knk=(pkl−thd)/bgl”.
Furthermore, based on the value of the knocking strength knk, a knocking retard amount rtd is calculated by the equation of “rtd=knk×K2”, and an ignition timing is changed to the retard side (that is, the side of delaying an ignition timing) by the knocking retard amount rtd.
Where, K2 is a predetermined coefficient for converting a knocking strength knk to a knocking retard amount rtd.
By the above-described series of processing, when the occurrence of knocking is determined based on the vibration waveform of the internal combustion engine to be detected by a knocking sensor, the ignition timing is corrected to the lag side in accordance with the magnitude of vibration level by the knocking, thus suppressing the occurrence of knocking.
However, depending on the operation state of the internal combustion engine, regardless of the presence or absence of the occurrence of knocking, a noise vibration to take place by the operation of any electric or mechanical operating member (for example, fuel injection valve, intake valve or exhaust valve) provided at an internal combustion engine may be superimposed on the vibration waveform detected by the knocking sensor in some cases.
In such cases, the knocking sensor may detect these noise vibrations to erroneously determine the occurrence of knocking, or may calculate a knocking strength with including a noise vibration even if the occurrence of knocking can be correctly determined.
Therefore, a problem exits in the “calculation of a knocking retard amount comes to be incorrect, and the output reduction or uncomfortable output change of the internal combustion engine arises.”
Accordingly, in the Japanese Patent Publication (unexamined) No. 207491/2006 or the Japanese Patent Publication (unexamined) No. 307709/2006, proposed is a method of removing noises that may superimpose on a vibration waveform a knocking sensor detects, thus to achieve precision improvements in knocking detection.
In the Japanese Patent Publication (unexamined) No. 207491/2006, proposed is a method in which the occurrence period of noise vibration is estimated based on the timing of driving a fuel injection valve, being one of noise sources, and in the case that the occurrence period of noise vibration is superimposed on the knocking detection period, the occurrence period of noise vibration in the knocking detection period is masked.
Thus, even in the case that a noise vibration takes place in the knocking detection period, the erroneous determination of knocking due to superimposition of noise vibration is prevented.
In the Japanese Patent Publication (unexamined) No. 307709/2006, proposed is a method in which the form of a noise vibration to take place by the operation of an intake valve, being one of noise sources, has preliminarily been stored; pattern matching between a vibration waveform having been detected in a knocking detection period and the form of noise vibration having preliminarily been stored is made to specify the occurrence period of noise vibration; and of the vibration waveforms having been detected in the knocking detection period, the vibration level due to the occurrence of noise is subtracted from the vibration waveform of the occurrence period of noise vibration having been specified (that is, a noise vibration component is removed from a vibration waveform having been detected in the knocking detection period).
In this manner, even in the case that any noise vibration takes place in the knocking detection period, the “erroneous determination of knocking” due to superimposition of noise vibration is prevented.
However, by the method described in the Japanese Patent Publication (unexamined) No. 207491/2006, the vibration waveform in the occurrence period of noise vibration of the knocking detection period comes to be masked.
Therefore, a problem exists in that in the case that the vibration waveform to take place due to occurrence of knocking and the occurrence period of noise vibration are overlapped in the same timing, the vibration waveform to take place due to the occurrence of knocking is masked as well and thus knocking cannot be detected.
Furthermore, by the method described in the Japanese Patent Publication (unexamined) No. 307709/2006, the vibration waveform having been detected and the form of noise vibration are brought in pattern matching to specify the occurrence period of noise vibration.
Therefore, another problem exists in that in the case that the vibration waveform to take place due to the occurrence of knocking and the occurrence period of noise vibration are overlapped in the same timing, the specification of noise vibration by the pattern matching of waveform becomes difficult, resulting in the erroneous determination of knocking, or even if the occurrence of knocking is correctly determined, a knocking strength with including a noise vibration will be calculated.